There are a wide variety of devices for presenting information in a manner designed to attract attention. One such device utilizes an array of discrete elongated three-sided sign elements arranged side-by-side to form scenes. The scenes may include messages, pictures, and advertisements etc. The device has a mechanism for rotating the three-sided sign elements in 120.degree. increments, thereby displaying each of the three different panels of the three-sided sign elements sequentially. The rotating mechanism typically involves a system of shafts, bearings, mounts and motors arranged to achieve the desired rotation.
An adaptation of the device is one in which the array of discrete elongated three-sided sign elements are made up of three distinct panels which have scenes on both sides of the panels. That is, each element is still triangular, but each side (i.e., panel) of the triangle rotates 180.degree., doubling the number of different scenes. The device has a mechanism to rotate the three-sided sign elements so that each of the three outer surfaces of the sign are displayed sequentially. As well, during each 120.degree. incremental rotation, one of the three sign elements is rotated 180.degree. around its own axis such that the scene that is on the inner surface of the panel is moved to the outer surface of the sign element. Thus, two 360.degree. rotations of the three-sided elements will complete the display of all six panel sides.
As described in U.S. Pat. No. 4,274,218 to Harvey, to enable the 180.degree. rotation of one panel, the two other panels are oscillated to avoid interference with adjacent panels. The oscillation of the two panels is required so that there is adequate clearance from adjacent panels for the 180.degree. rotation of the "flipping" panel. This action requires a complex dual cam system which must be precisely synchronized to work effectively.
As part of most of these systems, a crank arm may be used to impart rotary motion to a carrier shaft, to which are attached the sign elements. To attach the crank arm to the carrier shaft, a small hole is drilled through the side of the carrier shaft. A roll pin is then driven through a common hole in the crank arm and the carrier shaft. However, the carrier shaft is typically made of polymer plastic and is prone to cracking at the connection hole. The cracking can cause undesirable play or slop in the panel movement and can cause interference with adjacent panels.
These devices also have panel holders which are used to attach the panels to the rotation and display mechanism. To attach the panels to the panel holders, the panels are usually sandwiched between two metal clips and glued or fastened therein. The metal clips are then slid into the panel holders at the top of the display and then attached to spring-loaded clips at the bottom to provide tension to stretch the panels and maintain alignment. Gluing the panels is labor-intensive, and the panels are susceptible to separation from the metal clips due to poor panel-to-metal adhesion in the gluing process. As well, installation of the metal clips into the panel holders is labor-intensive and requires a specially trained individual to assure alignment.
In addition, these devices have drive systems which rotate the sign elements. Typically, two synchronous motors are employed to drive the cam follower mechanism. One motor is usually mounted adjacent to the top drive assembly, while the other is usually mounted adjacent to the bottom drive assembly. With this configuration, it can be difficult to synchronize the motion of the two motors so that the cams are driven at precisely the same rate and time and the panels are precisely aligned.
Further, the drive systems have no internal means to respond to or deal with either an internal mechanical malfunction or an exterior power failure. If the drive mechanism loses power between indexes, the unit will stop with the panels "in between" their display position. When the power is reapplied, the drive mechanism will advance the panels another 120.degree. and the device will be in between display positions again.
Currently, the cam assemblies that create the unique rotary and angular movement of the panels are made with a polymer utilizing injection molding. Each individual molded polymer cam is precisely mounted in an extruded aluminum "inter-frame." Two opposed cam assemblies are required for each array of prisms. The production of the cam and inner frame is time consuming and costly. Additionally, over time, the molded polymer cam sometimes becomes brittle and discolored, which makes the cam unattractive and subject to failure.
What is needed is a simple and effective mechanism that allows the panels of a three-sided sign element to be rotated such that all six sides of the panels can be viewed; a method for attaching a carrier shaft to a drive gear which holds the crank arm securely without cracking the carrier shaft; a way to attach panels to panel holders which is easy and durable; a synchronized drive mechanism; a way to ensure that the drive mechanism is always able to know where to stop such that the sign elements are properly displayed; and a cam assembly that is easier to build and will not break down over time.